The present invention is directed to a hypodermic syringe barrel and needle cannula assembly that is capable of being dry heat sterilized at high temperatures. The invention is more particularly directed to a hypodermic syringe barrel and needle cannula assembly that is capable of being dry heat sterilized at temperatures of greater than about 250xc2x0 C. and up to about 350xc2x0 C. in which the assembly comprises a syringe barrel, a needle cannula and a bonding material, where the bonding material fills a portion of the passageway into which the needle cannula is placed and thereby immobilizes and affixes the needle cannula to the tip of the syringe barrel. The selected bonding material is stable above about 250xc2x0 C. and cures to provide a transparent bond. The amount of bonding material used is pre-selected, preferably in relation to the interference length of the passageway, to provide the assembly with post-sterilization needle pullout strength of at least about 30 newtons.
Hypodermic syringes typically include an elongate cylindrical barrel having opposed proximal and distal ends and at least one chamber in between suitable for holding a substance such as a fluid medicament, drug or vaccine. The proximal end is open to allow the introduction of a plunger and may include a flange portion that functions as a finger hold. The distal end typically forms a tip that is closed except for a narrow passageway extending from the barrel chamber through the tip to the tip end and the exterior. A needle cannula is attached to the tip of the barrel directly within the passageway or indirectly via a needle holder. When the needle cannula is affixed into the passageway, it is typically attached with an adhesive.
Syringes with needle cannulas affixed with an adhesive are characterized by a dimension known as the xe2x80x9cinterference lengthxe2x80x9d that defines that portion of the passageway measured from the tip end of the syringe barrel to the bottom end of the affixed-needle cannula. Prior art syringes are generally known to have an interference length of about 5 to 10 millimeters.
Dry heat sterilization at high temperatures is the preferred methodology for sterilizing glass and steel medical device products including syringes primarily due to its ability to destroy or inactivate microbial pyrogens and bacterial endotoxins that may have been left in the syringes during manufacture or processing. The preferred dry heat sterilization temperature is in the range of 250xc2x0 C. to 350xc2x0 C.
Prior art syringe barrel and needle cannula assemblies, however, could not survive temperatures approaching 250xc2x0 C., primarily due to incineration and vaporization of the adhesives that were used to retain the needle cannulas in the syringe tips. The degradation processes of those adhesives have resulted in broken tips and/or loss of needle pullout strength. Additionally, at temperatures above about 180xc2x0 C., most of the adhesives used in the assemblies exhibited coloration due to the heat, resulting in rejections based mainly on aesthetics. Until now, it has been necessary to sterilize hypodermic syringe barrel and needle cannula assemblies at substantially lower temperatures.
Accordingly, due to the incumbent advantages of high temperature dry heat sterilization, there has remained an on-going need to develop a hypodermic syringe barrel and needle assembly capable of being dry heat sterilized at temperatures of greater than about 250xc2x0 C. without degradation to the adhesive used to affix the needle cannula to the syringe barrel.
The present invention is a hypodermic syringe barrel and needle cannula assembly capable of withstanding high temperature dry heat sterilization/-depyrogenation at temperatures of at least about 250xc2x0 C. and up to about 350xc2x0 C. As contemplated in the present invention, the needle cannula is affixed within the tip of the syringe barrel with a bonding material. The syringe barrel and needle cannula assembly (referred to herein as the xe2x80x9cbarrel assemblyxe2x80x9d or the xe2x80x9cassemblyxe2x80x9d) is capable of being dry heat sterilized at temperatures of at least about 250xc2x0 C. and up to about 350xc2x0 C. without any substantial degradation to the bonding material or the assembly. More specifically, the barrel assembly of the present invention preferably uses a polymer-based bonding material that includes a polymerization initiator and remains stable at temperatures greater than about 250xc2x0 C. and up to about 350xc2x0 C. The bonding material fills a portion of the crevice region that is formed between the exterior surface of the needle cannula and the interior surface of the passageway. The amount of bonding material used is pre-selected to provide the assembly with post-sterilization needle pullout strength of at least about 30 newtons or average needle pullout strength of at least about 60 newtons. The amount of bonding material used in the crevice region is characterized by a dimension referred to herein as the xe2x80x9cbonding depthxe2x80x9d that defines the depth of the adhesive in the passageway measured from the tip end. In the present invention, the bonding depth is preferably in relation to the interference length (as noted above, the xe2x80x9cinterference lengthxe2x80x9d refers to the distance of the needle cannula within the passageway). While it is fully contemplated the bonding depth may vary with the outer dimension of the cannula, it is preferred that bonding depth be at least about 2 millimeters and up to about 100% of the interference length.